1. Technical Field
The present invention relates generally to a method and apparatus for recovering oil from oil shale, and more specifically to a method and apparatus for recovering oil from oil shale using plasma gasification to prevent damage to the environment from effluents and contaminated residues.
2. Background
Oil shale is a fine-grained sedimentary rock containing relatively large amounts of kerogen (a solid mixture of organic chemical compound), from which liquid hydrocarbons can be manufactured. The name oil shale is something of a misnomer as the rock is not necessarily a shale and the hydrocarbon in it is not truly oil. It has been common practice in the art to convert the kerogen in oil shale to synthetic crude oil through the chemical process of pyrolysis. When heated to a sufficiently high temperature, a vapor is driven off which is then distilled (retorted) to yield a petroleum-like shale oil.
Oil shale deposits are widely distributed all over the world. More than 600 deposits are known, and their prospective resources are estimated to be over 500 million tons. On dry weight basis, oil shale consist of 10-60 percent of organics, 20-70 percent carbonate minerals and 15 to 60 percent sandy, clay minerals. Oil shale deposits are found on all inhabited continents. Oil shale has gained attention as an energy resource as the price of conventional sources of petroleum has risen, and as a way to secure independence from external suppliers of energy.
While some have been able to extract oil from oil shale using destructive pyrolysis, no one has yet found a way to extract the oil in a commercially profitable manner. Typically, the costs of environmental remediation when added to the costs of extraction exceed the costs of securing crude oil from other deposits. Although many methods have successfully produced oil from oil shale using destructive pyrolysis at approximately $16 to $20/Bbl. (excluding costs of environmental remediation), the conundrum has been to extract the oil profitably without damaging the environment. That is, to be able to extract the oil while generating environmentally inert byproducts.
Oil shale contains both a solid hydrocarbonous mixture (kerogen) and minerals. Kerogen when heated (retorted) yields combustible gases, shale oil, and a solid residue called by different names, e.g., spent shale, retorted shale, processed shale or semicoke. Typically, solid waste of the thermal treatment process, semicoke, is discharged from the retort and disposed in an open dump. Open depositions of semicoke cause distribution of pollutants via air (dust) as well as via aqueous vectors (leaching by rainfall and snowmelt). Leachates from various spent shales have been studied by a number of investigators. Properties of spent shale vary widely with the retorting process, but in general they contain significant amounts of total dissolved solids, sulphate, carbonate, bicarbonate, and other inorganic ions, and lesser amounts of trace elements and organic compounds. Leaching of these materials leach into the surrounding soil has a negative impact on the environment. As such, such practices of dumping byproducts from oil shale processing has been widely discouraged. Thus, as the world has become more environmentally conscious, such oil shale extraction processes have been significantly limited.
Plasma gasification was first developed by NASA to test the ceramic re-entry tiles of the space shuttles. It involves the excitement of gaseous molecules using electricity, which results in a super-heated gas beyond that obtainable by merely heating the gas. Plasma is an ionized gas, i.e. a gas with free-roaming electrons that carries a current and generates a magnetic field. Plasma fields are observable in lightening. It is capable of producing temperatures, which exceed those on the surface of the sun, but can be designed to meet much lower temperature parameters. Neon lights, for example, are a form of plasma. Plasma gasification has primarily been used to date for the processing of municipal waste as an alternative to incineration. By gasifying the waste with plasma, a syngas is generated capable of driving syngas turbines to create electricity. The intense energy causes the molecules to dissociate one from the other and break apart leaving the elemental components of the molecules, a process known as “molecular dissociation.”
Syngas (from synthesis gas) is the name given to a gas mixture that contains varying amounts of carbon monoxide and hydrogen generated by the gasification of a carbon based fuel to a gaseous product with a heating value. Examples include the gasification of waste-to energy in municipal and private waste gasification facilities, but can include any carbonaceous material, e.g. “bricks” derived from the production of methanol, animal wastes, old tires or even coal. Syngas consists primarily of carbon monoxide, carbon dioxide and hydrogen and has less than half the energy density of natural gas. Syngas is combustible and often used as a fuel source or as an intermediate for the production of other chemicals. Syngas for use as a fuel is most often produced by gasification of coal or municipal waste. The syngas produced in large waste-to-energy gasification facilities is used as fuel to generate electricity.
Plasma gasification has also been used to remediate soils contaminated with hydrocarbons, resulting in the complete removal of the contaminating hydrocarbons. Recently, Solena Group, Inc., has used plasma gasification to remediate dirty coal plants and produce electricity using the syngas generated from virtually any carbon resource, including, among other fuels, municipal waste, coal and “bricks” which result from ethanol plants where ethanol is derived from renewable feedstocks, e.g., corn stalks. While the Solena Group plasma gasification uses water-cooled electrodes to emit the electrical energy into the gas, MIT has developed a plasma gasification technology that utilizes microwave energy to excite the plasma.
In order to extract oil, gas and byproducts from pyrobituminous shale or other solid materials impregnated with hydrocarbons, some inventors, including among others, John B. Jones et al., U.S. Pat. No. 3,736,247 issued May 29, 1973, and Petroleo Brasileiro S. A. -Petrobras, of Rio de Janeiro, Brazil, U.S. Pat. No. 3,887,453 issued Jun. 3, 1975, developed and patented vertical kiln systems as shown and described in their respective patents, the entirety of which are incorporated herein by this reference and herein-after referenced as the “Paraho/Petrobras systems”. While the Paraho/Petrobras systems provide an efficient means of extracting hydrocarbons (95%+ of Fisher Assay), the systems do not adequately address the environmental issues that result from such an extraction process, namely, the creation of environmentally unacceptable byproducts and pollutants, whether from the initial heating process or in the spent shale.
Thus, there exists a need in the art to produce oil from oil shale without harmful or noxious emissions or effluents. There further exists a need to produce oil from oil shale in a manner that reduces thermal pollution, eliminates tailings piles, and reduces excessive excess water requirements (historically associated primarily with compacting the spent shale and planting over the spent shale) while purifying the water used in the production process. There is also a need to completely recover the oil in the oil shale. These and other advantages will be apparent from a reading of the following description of the invention and the appended drawings.